There is a
fairly recent thread on this, I just go by feel and try to not have too hard. I should read it again too. I don't think it puts strain the motor or any other part in the same way a too tight belt does. The belt sort of puts the motor axle off balance while presser bar tension is dow on the needle plate and the feed dogs move up on the fabric like they should. The experts will hopefully clarify. I have only had it almost all the way down on very difficult seams on heavy denim and duck, not often at all (like flat felled seams on jeans when you join pieces).